In general, battery terminals are utilized as an interface between a sealed battery container and an external device seeking electrical power. In sealed batteries containing liquid electrolyte, the battery terminal must be configured to prevent leakage of electrolyte to ensure the battery will not fail prematurely when called upon. This is especially important in today's business environment where such batteries are relied upon as power backups for large banks of computers. To prevent leakage of electrolyte around a battery terminal it is common to provide a plurality of annular rings extending around the head of the battery terminal, which is designed to be embedded in the wall of the container.
Battery terminals including annular rings on the head are typically formed from lead in a cold or hot forming process. In the hot forming process, a lead alloy is heated until it is in a molten state. The molten lead is then poured into a mold or casting and formed into a partially-finished or finished battery terminal. In the cold forming process a lead slug (typically at room temperature) is subjected to various pressing, punching and machining operations to create the finished battery terminal.
As mentioned above, the hot forming process requires that the lead be heated until it reaches the molten state and then subsequently poured into a multi-part mold until it cools. This is disadvantageous in that melting the lead alloy may create undesirable porosity in the finished battery terminal and is expensive to implement in an environmentally safe manner. In addition, the multi-part mold used in the hot forming process imposes design constraints on the battery terminal in that the various elements of the battery terminal must be shaped so that the battery terminal can be removed from the mold once the lead alloy has cooled. Thus, battery terminals formed by this process with annular rings must not include any undercuts or overhangs.
Existing methods of cold forming a battery terminal from a lead slug require a number of individual steps. In one known method a lead slug is first modified in a preform station and then subsequently formed into a finished battery terminal in a final forming press having a split die. Alternatively, in a second known method a lead slug is formed into a semi-finished battery terminal in a first station having a split die and then subsequently machined to create a finished battery terminal.
As with the multi-part molds of the hot forming process, the use of a split die to form a battery terminal with annular rings in the cold forming process limits the shape of the annular rings. In particular, the annular rings must not have any undercut or overhang because that would make it impossible to remove the battery terminal after forming is complete.
Most battery terminals formed today by the above-described processes have annular rings with substantially rectangular cross-sectional shapes because this simplifies manufacture thereof and thus reduces costs. It has been found, however, that annular rings having such simple profiles can result in leakage of electrolyte as the plastic material surrounding the battery terminal shrinks over time. By contrast, battery terminals having annular rings with undercuts or overhangs are less likely to leak as the plastic material shrinks over time because the more complex profile provides an improved labyrinth seal.
Consequently, it would be desirable to have a simplified process for cold forming a battery terminal with annular rings having undercuts or overhangs to improve sealing properties of the annular rings.